Comparison of a Squirrel-Cage and a Slip Ring (or Phase Wound)

Induction Motors 

The properties between a squirrel-cage and a slip ring (or phase wound) induction motors are different. The comparison is important to understand their proper utilization. Some differences are as follows by their properties –

  • Starting  – The starting property of a squirrel cage in an induction motor needs to be started with a starter named star-delta. In addition, it is also used to eliminate the hazards like rings, brush gear, slip, etc.

In phase wound induction motor, brush gear, slip rings, starting resistance and short circuiting device etc are required.

  • Overhang – The overhang property is less in a squirrel cage induction motor and it is large in phase wound motor.
  • Space factor in slots – The space factor in slots of Squirrel cage is better, while this has a poor condition in the slip ring induction motor.
  • Cooling – In squirrel-cage, the losses can be degenerated in a proper way as the used rings are actually bars that provide sufficient space to run a fan. On the other hand, in a slip ring induction motor overhang takes a large space and thus there is very less space available for a good cooling fan services. So, in this case cooling is not quite efficient.
  • Efficiency – Squirrel cage has a higher efficiency, but phase wound has a relatively lower efficiency.
  • Starting Torque – If the motor of squirrel cage is plain, then the working ability of a starting torque is very poor. In case of wound phase, the starting torque ability can be increased in each phase by inserting of external resistance.
  • Copper losses – As there is less overhang and proper space factor, so copper losses are minimal in a squirrel cage. But, in wound phase, there is more copper loss.
  • Maintenance – Less maintenance is required in Squirrel Cage, but the phase wound requires more maintenance.
  • Cost – The cost of squirrel cage is cheaper, but a slip ring is relatively expensive.


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